Germanium-containing release layer for transfer of a silicon layer to a substrate

ABSTRACT

A germanium-containing layer is deposited on a single crystalline bulk silicon substrate in an ambient including a level of oxygen partial pressure sufficient to incorporate 1%-50% of oxygen in atomic concentration. The thickness of the germanium-containing layer is preferably limited to maintain some degree of epitaxial alignment with the underlying silicon substrate. Optionally, a graded germanium-containing layer can be grown on, or replace, the germanium-containing layer. An at least partially crystalline silicon layer is subsequently deposited on the germanium-containing layer. A handle substrate is bonded to the at least partially crystalline silicon layer. The assembly of the bulk silicon substrate, the germanium-containing layer, the at least partially crystalline silicon layer, and the handle substrate is cleaved within the germanium-containing layer to provide a composite substrate including the handle substrate and the at least partially crystalline silicon layer. Any remaining germanium-containing layer on the composite substrate is removed.

BACKGROUND

The present disclosure relates to a method of forming a semiconductorstructure, and more particularly to a method of forming a semiconductorstructure including a transferred semiconductor layer, and structuresfor effecting the same and formed by the same.

A substrate including a thin silicon layer can be formed by employing ahydrogen-containing cleavage layer. For example, hydrogen ions (protons)can be implanted into a bulk silicon substrate to form ahydrogen-containing layer at a constant depth from a top surface of thebulk silicon substrate. A handle substrate is bonded to the top surfaceof the bulk silicon substrate, and the bulk silicon substrate issubsequently cleaved at the hydrogen-containing layer so that a thinsilicon layer above the hydrogen-containing layer is “transferred” tothe handle substrate to form a new substrate, which is an assembly ofthe handle substrate and the transferred thin silicon layer. Theremaining portion of the bulk substrate is planarized by chemicalmechanical planarization and re-used to provide another thin siliconlayer for another layer transfer process until the thickness of the bulksubstrate becomes too thin to be employed for layer transfer purposes.

The method of forming a substrate including a thin silicon layeremploying hydrogen implantation is subject to many limitations. First, ahydrogen-containing layer must be formed through hydrogen implantation.Because of inherent depth distribution of the implanted hydrogen ions, ahigh dose of hydrogen ions must be implanted into the bulk siliconsubstrate to be able to induce cleavage at the hydrogen-containinglayer. Because the vertical distribution range of the hydrogen ionsincreases with increasing depth of implantation, higher dose of hydrogenions is needed as the depth of the hydrogen-containing layer increases.

Further, due to the propensity of bulk silicon substrates to cleavealong major crystallographic planes, cleavage along only somecrystallographic orientations of a silicon crystal produces cleancleavage planes with atomic planarity, while cleavage along othercrystallographic orientations can produce cleavage planes that includefacets and/or rough surfaces that need to be planarized, for example, bychemical mechanical planarization.

Yet further, the bulk substrate after cleavage needs to be planarizedbefore re-usage. In addition, any modification to the dopantconcentration in the transferred layer requires additional processesthat include implantation or plasma treatment and dopant activation by ahigh temperature anneal.

Thus, a process of forming a transferred silicon layer without employinghydrogen ion implantation is desired.

BRIEF SUMMARY

A germanium-containing layer is deposited on a single crystalline bulksilicon substrate in an ambient including a level of oxygen partialpressure sufficient to incorporate 1%-50% of oxygen in atomicconcentration. The thickness of the germanium-containing layer may belimited to facilitate some degree of epitaxial alignment with theunderlying silicon substrate. Optionally, a graded germanium-containinglayer including a graded silicon-germanium alloy can be grown on, orreplace, the germanium-containing layer. An at least partiallycrystalline silicon layer is subsequently deposited on thegermanium-containing layer. A handle substrate is bonded to the at leastpartially crystalline silicon layer. The assembly of the bulk siliconsubstrate, the germanium-containing layer, the at least partiallycrystalline silicon layer, and the handle substrate is cleaved withinthe germanium-containing layer to provide a composite substrateincluding the handle substrate and the at least partially crystallinesilicon layer. Any remaining portion of the germanium-containing layeron the composite substrate is removed.

According to an aspect of the present disclosure, a method of forming asemiconductor structure includes: growing a germanium-containing layeron a single crystalline silicon substrate; growing an at least partiallycrystalline silicon layer on the germanium-containing layer; bonding ahandle substrate to the at least partially crystalline silicon layer;and cleaving an assembly of the handle substrate and the at leastpartially crystalline silicon layer off the single crystalline siliconsubstrate along a plane in the germanium-containing layer.

According to another aspect of the present disclosure, a semiconductorstructure including a material stack, which includes: a singlecrystalline silicon substrate; a germanium-containing layer contactingthe single crystalline silicon substrate; an at least partiallycrystalline silicon layer located on the germanium-containing layer; anda handle substrate bonded to the at least partially crystalline siliconlayer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A-1F are vertical cross-sectional views of a first exemplarysemiconductor structure according to a first embodiment of the presentdisclosure.

FIG. 2A-2F are vertical cross-sectional views of a second exemplarysemiconductor structure according to a second embodiment of the presentdisclosure.

FIG. 3A-3F are vertical cross-sectional views of a third exemplarysemiconductor structure according to a third embodiment of the presentdisclosure.

FIG. 4A-4F are vertical cross-sectional views of a fourth exemplarysemiconductor structure according to a fourth embodiment of the presentdisclosure.

FIG. 5 is a graph of an X-ray diffraction data from a first sampleaccording to the first embodiment of the present disclosure as afunction of 2θ.

FIG. 6 is a graph of an X-ray diffraction data from a second sampleaccording to the second embodiment of the present disclosure as afunction of 2θ.

FIG. 7 is a graph of an X-ray diffraction data from a third sampleincluding a polysilicon film as a function of 2θ.

FIG. 8 is a graph illustrating data from a secondary ion massspectroscopy (SIMS) run on the second sample according to the secondembodiment of the present disclosure.

FIG. 9 is a scanning electron micrograph (SEM) of a broken portion ofthe first sample along a vertical cleavage plane without cleaving alongthe oxygen-containing germanium layer.

FIG. 10 is a scanning electron micrograph (SEM) of a portion of thefirst sample, which was cleaved along the oxygen-containing germaniumlayer and includes the bulk silicon substrate and a portion of theoxygen-containing germanium layer.

DETAILED DESCRIPTION

As stated above, the present disclosure relates to a method of forming asemiconductor structure including a transferred semiconductor layer, andstructures for effecting the same and formed by the same, which are nowdescribed in detail with accompanying figures. Throughout the drawings,the same reference numerals or letters are used to designate like orequivalent elements. The drawings are not necessarily drawn to scale.

As used herein, a “textured crystalline layer” is a polycrystallinelayer including grains, in which a predominant portion of the grainshave the same set of crystallographic orientations. A “predominantportion” of an element refers to more than 50% in volume of the element.Likewise, as used herein, a “polycrystalline layer” is a more generalterm that includes both textured crystalline layers and crystallinelayers including grains with a mix of crystallographic orientations withno single dominant orientation.

As used herein, an “at least partially crystalline layer” is a layerthat is either a single crystalline layer, a textured crystalline layer,or polycrystalline layer.

As used herein, an “at least partially crystalline silicon layer” is anat least partially crystalline layer including intrinsic silicon ordoped silicon.

Referring to FIG. 1A, a first exemplary semiconductor structureaccording to a first embodiment of the present disclosure includes asingle crystalline semiconductor substrate 10. In one embodiment, thesingle crystalline semiconductor substrate 10 consists of intrinsicsilicon or doped silicon. In one embodiment, the single crystallinesilicon substrate 10 is a bulk silicon. In this embodiment, the singlecrystalline silicon substrate 10 is thick enough to allow mechanicalhandling of the single crystalline silicon substrate 10 withoutbreakage, and can have a thickness from 200 microns to 2,000 microns. Inanother embodiment, the single crystalline silicon substrate 10 can beattached to another substrate that facilitates handling of the singlecrystalline silicon substrate 10. For example, the single crystallinesilicon substrate 10 can be attached to an insulating substrate or aconductive substrate. In this embodiment, the single crystalline siliconsubstrate 10 can have a thickness from 5 microns to 2,000 microns.

The surface normal of a planar top surface of the single crystallinesilicon substrate 10 can have any crystallographic orientation. In oneembodiment, the surface normal of the planar top surface of the singlecrystalline silicon substrate 10 can have a “major crystallographicorientation,” which is defined herein as an orientation having a set ofMiller indices in which each Miller index in the set of Miller indiceshas an absolute value that does not exceed 6. In another embodiment, thesurface normal of the planar top surface of the single crystallinesilicon substrate 10 can have a “non-major crystallographicorientation,” which is defined herein as an orientation having a set ofMiller indices in which at least one Miller index in the set of Millerindices has an absolute value that exceeds 6. Thus, the orientation ofthe surface normal of a planar top surface of the single crystallinesilicon substrate 10 is not limited in any way. Non-conventional surfaceorientations having a “high Miller index,” i.e., a Miller index havingan absolute value that exceeds 6, can be provided on the singlecrystalline silicon substrate 10 by angled polishing on a conventionalsingle crystalline silicon substrate having “low Miller indices,” i.e.,Miller indices having absolute values that do not exceed 6.

Referring to FIG. 1B, a germanium-containing layer 20 is grown directlyon the top surface of the single crystalline silicon substrate 10,preferably with at least some degree of epitaxial alignment. The degreeof epitaxial alignment between the germanium-containing layer 20 and thesingle crystalline silicon substrate 10 may be complete or incomplete,depending on embodiments. In one embodiment, the germanium-containinglayer 20 is a single crystalline layer having an epitaxial alignmentwith the single crystalline silicon substrate 10 at an atomic level. Inanother embodiment, the germanium-containing layer 20 is a texturedcrystalline layer in which grains are predominantly oriented in adirection providing epitaxial alignment with the single crystallinestructure of the single crystalline silicon substrate 10 at an atomiclevel. In this embodiment, a predominant portion of the grains of thegermanium-containing layer 20 has the same set of crystallographicorientations as the single crystalline silicon substrate 10. In yetanother embodiment, germanium-containing layer 20 may bepolycrystalline.

The germanium-containing layer 20 is grown in an ambient having anoxygen partial pressure at a level that incorporates oxygen into thegermanium-containing layer 20 at an atomic concentration between 1% and50%, and typically between 2% and 20%. The oxygen partial pressure canbe provided by residual gases in a high vacuum environment having a basepressure of 10⁻⁶ Torr to 100 mTorr, and typically from 10⁻⁵ Ton and 10mTorr. Alternately, the oxygen partial pressure can be provided bysupplying an oxygen-containing gas such as oxygen, ozone, or carbondioxide in an ultrahigh vacuum environment having a base pressure lessthan 10⁻⁶ Torr. Yet alternately or in addition, the germanium-containinglayer 20 can be deposited in an environment having a low oxygen partialpressure such that the germanium-containing layer 20 has an atomicconcentration of oxygen less than 1% as deposited. In this case, thegermanium-containing layer 20 can be exposed to an oxygen-containingambient to allow adsorption of oxygen and subsequent incorporation ofoxygen into the germanium-containing layer 20 at an atomic concentrationbetween 1% and 50%, and typically between 2% and 20%.

In one embodiment, the germanium-containing layer 20 can have asubstantially constant germanium concentration at an atomicconcentration from 30% to 99%. The germanium concentration is“substantially constant” because statistical variations in germaniumconcentration is inherently present due to the statistical nature ofcomposition of the germanium-containing layer 20. In one case, thegermanium-containing layer 20 can include germanium and oxygen, and thesum of the atomic concentration of germanium and the atomicconcentration of oxygen is greater than 99%. The germanium-containinglayer 20 may consist essentially of germanium and oxygen, and the sum ofthe atomic concentration of germanium and the atomic concentration ofoxygen is greater than 99%. In another case, the germanium-containinglayer 20 can include germanium, silicon, and oxygen, and the sum of theatomic concentration of germanium, the atomic concentration of silicon,and the atomic concentration of oxygen is greater than 99%. Thegermanium-containing layer 20 may consist essentially of germanium,silicon, and oxygen, and the sum of the atomic concentration ofgermanium, the atomic concentration of silicon, and the atomicconcentration of oxygen is greater than 99%. In yet another case, thegermanium-containing layer 20 can include germanium, silicon, at leastanother atom, and oxygen, and the sum of the atomic concentration ofgermanium, the atomic concentration of silicon, the atomic concentrationof the at least another atom, and the atomic concentration of oxygen isgreater than 99%. The germanium-containing layer 20 may consistessentially of germanium, silicon, at least another atom, and oxygen,and the sum of the atomic concentration of germanium, the atomicconcentration of silicon, the atomic concentration of the at leastanother atom, and the atomic concentration of oxygen is greater than99%. The at least another atom can be carbon, a p-type dopant such asboron, gallium, or indium, an n-type dopant such as phosphorus, arsenic,or antimony, any other impurity atoms such as nitrogen, fluorine,hydrogen, or argon, or a combination thereof.

In another embodiment, the germanium-containing layer 20 can includesilicon, germanium, and oxygen. The atomic concentration of germaniumdecreases in the germanium-containing layer 20 with the distance fromthe single crystalline silicon substrate 10. Thus, the atomicconcentration of germanium in the germanium-containing layer 20 hasvariable values, which can be in a range from 0% and 99%. In this case,the atomic concentration of germanium in the graded germanium-containinglayer 20 has a maximum value that is at least 50%, which occurs at ornear the interface with the single crystalline silicon substrate 10. Inone case, the germanium-containing layer 20 can include germanium,silicon, and oxygen, and the sum of the atomic concentration ofgermanium, the atomic concentration of silicon, and the atomicconcentration of oxygen is greater than 99% in each location within thegermanium-containing layer 20. The germanium-containing layer 20 mayconsist essentially of germanium, silicon, and oxygen, and the sum ofthe atomic concentration of germanium, the atomic concentration ofsilicon, and the atomic concentration of oxygen is greater than 99% ineach location within the germanium-containing layer 20. In another case,the germanium-containing layer 20 can include germanium, silicon, atleast another atom, and oxygen, and the sum of the atomic concentrationof germanium, the atomic concentration of silicon, the atomicconcentration of the at least another atom, and the atomic concentrationof oxygen is greater than 99% in each location within thegermanium-containing layer 20. The germanium-containing layer 20 mayconsist essentially of germanium, silicon, at least another atom, andoxygen, and the sum of the atomic concentration of germanium, the atomicconcentration of silicon, the atomic concentration of the at leastanother atom, and the atomic concentration of oxygen is greater than 99%in each location within the germanium-containing layer 20. The at leastanother atom can be carbon, a p-type dopant such as boron, gallium, orindium, an n-type dopant such as phosphorus, arsenic, or antimony, anyother impurity atoms such as nitrogen, fluorine, hydrogen, or argon, ora combination thereof.

In one embodiment, germanium-containing layer 20 is at least partiallyepitaxial. The thickness of the germanium-containing layer 20 ismaintained not to exceed the critical thickness at which the epitaxialalignment between the single crystalline silicon substrate 10 and thegermanium-containing layer 20 is destroyed through stress relaxation.The oxygen content of germanium-containing layer 20 is also kept low(e.g., 1-3%) to help preserve epitaxy. In another embodiment, thethickness of the germanium-containing layer 20 may be less than, thesame as, or exceed the critical thickness at which the epitaxialalignment between the single crystalline silicon substrate 10 and thegermanium-containing layer 20 is destroyed through stress relaxation. Ifthe thickness of the germanium-containing layer 20 exceeds the criticalthickness, the germanium-containing layer 20 may develop dislocationstherein.

If the thickness of the germanium-containing layer 20 does not exceedthe critical thickness, the thickness of the germanium-containing layer20 is between 5 nm and 80 nm, and preferably between 10 nm and 60 nm,although lesser and greater thicknesses can also be employed dependingon the concentration of germanium provided that at least some epitaxialalignment between the germanium-containing layer 20 and the singlecrystalline silicon substrate 10 is maintained.

The germanium-containing layer 20 can be deposited by chemical vapordeposition (CVD), vacuum evaporation, or atomic layer deposition (ALD).The deposition temperature is set at a temperature that providessufficient surface diffusion to germanium atoms and silicon atoms, ifsilicon is incorporated in the germanium-containing layer 20, and anyother atoms, if any other atoms are incorporated into thegermanium-containing layer 20. For example, the deposition temperaturecan be 450° C. to 900° C., and typically from 500° C. to 700° C. Thepressure of the deposition chamber can vary depending on the depositionprocess employed. In general, chemical vapor deposition processes employdeposition conditions including a total pressure from 0.1 Torr to 10Torr, and typically from 0.2 Torr to 5 Torr. A predominant portion ofthe total pressure is the partial pressure of a carrier gas. If vacuumevaporation or atomic layer deposition is employed, the depositionpressure is typically from 10⁻⁶ Torr to 10⁻³ Torr, depending on the basepressure of the deposition system and whether oxygen gas is flowed intothe deposition chamber in addition to residual oxygen gases inherentlypresent in any vacuum chamber having a finite (non-zero) base pressure.In case atomic layer deposition is employed, at least one reactant gasand oxygen gas can be alternately flowed into a deposition chamber withoptional adjustments to the temperature of the single crystallinesilicon substrate 10 to control the amount of oxygen incorporated intothe germanium-containing layer 20.

In case chemical vapor deposition is employed, the single crystallinesilicon substrate 10 is placed in a vacuum environment, of which thebase pressure can vary as discussed above. Low pressure chemical vapordeposition (LPCVD) process or plasma enhanced chemical vapor deposition(PECVD) may be employed. Energy to decompose one or more reactant gasesis provided by thermal energy, whereas energy to decompose one or morereactant gases is provided by plasma energy. A germanium-containingreactant gas, which includes at least one atom of germanium, is flowedinto the deposition chamber. Exemplary germanium-containing reactantgases include GeH₄, GeH₂Cl₂, GeCl₄, and Ge₂H₆. If silicon isincorporated into the germanium-containing layer 20, asilicon-containing reactant gas including at least one atom of silicon,e.g., SiH₄, SiH₂Cl₂, SiHCl₃, SiCl₄, and Si₂H₆, can be flowed into thedeposition chamber. Atomic layer deposition can employ the samereactants and/or dopants as chemical vapor deposition.

If vacuum evaporation is employed, germanium and/or silicon can beevaporated from an evaporation source, which can be an electron beamsource or an effusion cell. Typically, the evaporation source is heatedat or near the melting temperature of the source material, i.e., themelting temperature of germanium or the melting temperature of silicon.Oxygen can be provided by background level residual oxygen in a vacuumsystem having a base pressure greater than 10⁻⁶ Torr. Alternatively orin addition, oxygen gas can be continually or intermittently providedinto the deposition chamber from an oxygen source such as a mass flowcontroller connected to an oxygen tank. Alternatively or in addition,oxygen can be provided to the top surface of the germanium-containinglayer 20 and incorporated therein by diffusion.

Optionally, the material stack including the single crystalline siliconsubstrate 10 and the germanium-containing layer 20 may be maintained atan elevated temperature for a period of time to enhance the degree ofepitaxial alignment between the single crystalline silicon substrate 10and the germanium-containing layer 20 and/or to repair crystallinedefects in the germanium-containing layer 20. Because silicon andgermanium have the same crystal structures, a crystallinegermanium-containing layer 20 would be expected to have acrystallographic orientation epitaxially related to that of the singlecrystalline silicon substrate 10.

Referring to FIG. 1C, an at least partially crystalline silicon layer 30having at least some degree of crystallinity is grown directly on thetop surface of the germanium-containing layer 20. In one embodiment, theat least partially crystalline silicon layer 30 is a single crystallinelayer having a complete epitaxial alignment with thegermanium-containing layer 20 at an atomic level. In another embodiment,the at least partially crystalline silicon layer 30 is a texturedcrystalline layer in which grains are predominantly oriented in adirection providing epitaxial alignment with the single crystallinestructure of the germanium-containing layer 20 at an atomic level. Inthis embodiment, a predominant portion of the grains of the at leastpartially crystalline silicon layer 30 has the same set ofcrystallographic orientations as the germanium-containing layer 20. Inyet another embodiment, the at least partially crystalline silicon layer30 is a textured crystalline layer in which grains are predominantlyoriented in a direction providing epitaxial alignment with a texturedcrystalline structure of the germanium-containing layer 20 at an atomiclevel. In this embodiment, a predominant portion of the grains of the atleast partially crystalline silicon layer 30 has the same set ofcrystallographic orientations as the germanium-containing layer 20.

The thickness of the at least partially crystalline silicon layer 30 isselected to apply sufficient stress to the germanium-containing layer 20to cause formation of a plurality of cavities 27 within thegermanium-containing layer 20 by the end of deposition of the at leastpartially crystalline silicon layer 30. The thickness of the at leastpartially crystalline silicon layer 30 needed to generate cavities 27within the germanium-containing layer 20 depends on the thickness of thegermanium-containing layer 20 and the germanium content and the oxygencontent in the germanium-containing layer 20. In general, the thicknessof the at least partially crystalline silicon layer 30 is at least equalto the thickness of the germanium-containing layer 20, and is typicallygreater than twice the thickness of the germanium-containing layer 20.In case the germanium-containing layer 20 includes silicon in additionto germanium and oxygen, the thickness of the at least partiallycrystalline silicon layer 30 can be greater than three times thethickness of the germanium-containing layer 20. Typically, the at leastpartially crystalline silicon layer 30 has a thickness that is greaterthan 100 nm. For example, the thickness of the at least partiallycrystalline silicon layer 30 can be from 100 nm to 500 nm, althoughlesser and greater thicknesses can also be employed.

The plurality of cavities 27 is formed during the epitaxial growth ofthe at least partially crystalline silicon layer 30, i.e., before thecompletion of deposition of the silicon material of the at leastpartially crystalline silicon layer 30. The lateral dimensions of theplurality of cavities 27 is on the same order of magnitude as thethickness of the germanium-containing layer 20. Typically, each cavityin the plurality of cavities has a maximum lateral dimension less than200 nm.

The at least partially crystalline silicon layer 30 is grown in a vacuumenvironment in which oxygen partial pressure is minimal or in an ambientin which oxygen partial pressure is minimized. Any oxygen incorporatedin the at least partially crystalline silicon layer 30 is maintainedbelow 5% in atomic concentration, and preferably below 2% in atomicconcentration, and most preferably as low as possible.

The at least partially crystalline silicon layer 30 can be deposited bychemical vapor deposition (CVD) or vacuum evaporation. The depositiontemperature is set at a temperature that provides sufficient surfacediffusion to silicon atoms. For example, the deposition temperature canbe from 500° C. to 1,100° C., and typically from 500° C. to 700° C. Thepressure of the deposition chamber can vary depending on the depositionprocess employed. In general, chemical vapor deposition processes employdeposition conditions including a total pressure from 0.1 Torr to 10Torr, and typically from 0.2 Torr to 5 Torr. A predominant portion ofthe total pressure is the partial pressure of a carrier gas such ashydrogen gas. If vacuum evaporation or atomic layer deposition isemployed, the deposition pressure is typically from 10⁻⁶ Torr to 10⁻³Torr.

In case chemical vapor deposition is employed, the stack of the singlecrystalline silicon substrate 10 and the germanium-containing layer 20is placed in a vacuum environment such that the top surface of thegermanium-containing layer 20 is exposed. Low pressure chemical vapordeposition (LPCVD) process or plasma enhanced chemical vapor deposition(PECVD) may be employed. A silicon-containing reactant gas including atleast one atom of silicon, e.g., SiH₄, SiH₂Cl₂, SiHCl₃, SiCl₄, andSi₂H₆, is flowed into the deposition chamber. The at least partiallycrystalline silicon layer 30 can be doped in-situ with p-type dopants orn-type dopants by concurrently flowing dopant gases such as B₂H₆, PH₃,AsH₃, SbH₃, or a combination thereof. If vacuum evaporation is employed,silicon can be evaporated from an evaporation source, which can be anelectron beam source or an effusion cell.

Optionally, the material stack including the single crystalline siliconsubstrate 10, the germanium-containing layer 20, and the at leastpartially crystalline silicon layer 30 may be maintained at an elevatedtemperature for a period of time to enhance the degree of epitaxialalignment between the germanium-containing layer 20 and the at leastpartially crystalline silicon layer 30 and/or to repair crystallinedefects in the at least partially crystalline silicon layer 30.

Referring to FIG. 1D, a handle substrate 40 is attached to the topsurface of the at least partially crystalline silicon layer 30, forexample, by bonding. The handle substrate 40 can include a dielectricmaterial layer, a conductive material layer, a polycrystallinesemiconductor material layer, a single crystalline semiconductormaterial layer, or a combination thereof. In non-limiting exemplarycases, the handle substrate 40 can be a glass substrate or a metalsubstrate. Any bonding method known in the art may be employed includinganodic bonding, in which an electrical bias voltage is applied acrossthe interface between the at least partially crystalline silicon layer30 and the handle substrate 40. Typically, the handle substrate 40 isthick enough to allow mechanical handling without significant risk ofbreakage. For example, the handle substrate 40 can have a thickness from200 microns to 5 mm, and typically from 500 microns to 1 mm, althoughlesser and greater thicknesses can also be employed.

Referring to FIG. 1E, the first exemplary semiconductor structure iscleaved along a plane, which is herein referred to as a “cleavageplane,” located within the germanium-containing layer 20. An upperassembly of the handle substrate 40 and the at least partiallycrystalline silicon layer 30 and an upper portion of thegermanium-containing layer 20, which is herein referred to as an upperepitaxial germanium-containing portion 27B, is cleaved off a lowerassembly including the single crystalline silicon substrate 10 and alower portion of the germanium-containing layer 20, which is hereinreferred to as a lower epitaxial germanium-containing portion 27A, alongthe cleavage plane.

Treatment of the first exemplary semiconductor structure by any chemicaltreatment, thermal treatment, or ion implantation is not necessarybecause the germanium-containing layer 20 is under stress induced by thelattice mismatch with the single crystalline silicon substrate 10 andthe at least partially crystalline silicon layer 30. Thus, mechanicalshear stress applied to the first exemplary semiconductor structure(i.e., twisting the upper assembly (40, 30, 20B) relative to the lowerassembly (10, 20A)) or mechanical tensile stress applied the firstexemplary semiconductor structure (i.e., pulling the upper assembly (40,30, 20B) away from the lower assembly (10, 20A)) can separate the upperassembly (40, 30, 20B) from the lower assembly (10, 20A).

Referring to FIG. 1F, the upper germanium-containing portion 27B isremoved selective to the at least partially crystalline silicon layer 30by an etch or planarization. The etch can be an isotropic etch such as awet etch employing hydrogen peroxide that removes germanium or asilicon-germanium alloy with a high atomic percentage of germanium(i.e., at least 30% of germanium in atomic concentration), or a dry etchsuch as a reactive ion etch that is selective to silicon. Alternately orin addition, chemical mechanical planarization can be employed to removethe upper germanium-containing portion 27B. The upper assembly at thispoint includes a stack of the handle substrate 40 and the at leastpartially crystalline silicon layer 30.

Referring to FIG. 2A, a second exemplary semiconductor structureaccording to a second embodiment of the present disclosure includes asingle crystalline silicon substrate 10, which is the same as the singlecrystalline silicon substrate 10 of the first embodiment.

Referring to FIG. 2B, a stack of a germanium-containing layer 20 and agraded germanium-containing layer 22 are grown on the single crystallineat least partially crystalline silicon layer 10. Each of thegermanium-containing layer 20 and the graded germanium-containing layer22 can be deposited by chemical vapor deposition, vacuum evaporation, oratomic layer deposition as described in the first embodiment.

The germanium-containing layer 20 includes oxygen at an atomicconcentration between 1% and 50%, and typically between 2% and 20%. Thegermanium-containing layer 20 has a substantially constant germaniumconcentration at an atomic concentration from 30% to 99%. In one case,the germanium-containing layer 20 can include germanium and oxygen, andthe sum of the atomic concentration of germanium and the atomicconcentration of oxygen is greater than 99%. The germanium-containinglayer 20 may consist essentially of germanium and oxygen, and the sum ofthe atomic concentration of germanium and the atomic concentration ofoxygen is greater than 99%. In another case, the germanium-containinglayer 20 can include germanium, silicon, and oxygen, and the sum of theatomic concentration of germanium, the atomic concentration of silicon,and the atomic concentration of oxygen is greater than 99%. Thegermanium-containing layer 20 may consist essentially of germanium,silicon, and oxygen, and the sum of the atomic concentration ofgermanium, the atomic concentration of silicon, and the atomicconcentration of oxygen is greater than 99%. In yet another case, thegermanium-containing layer 20 can include germanium, silicon, at leastanother atom, and oxygen, and the sum of the atomic concentration ofgermanium, the atomic concentration of silicon, the atomic concentrationof the at least another atom, and the atomic concentration of oxygen isgreater than 99%. The germanium-containing layer 20 may consistessentially of germanium, silicon, at least another atom, and oxygen,and the sum of the atomic concentration of germanium, the atomicconcentration of silicon, the atomic concentration of the at leastanother atom, and the atomic concentration of oxygen is greater than99%. The at least another atom can be carbon, a p-type dopant such asboron, gallium, or indium, an n-type dopant such as phosphorus, arsenic,or antimony, any other impurity atoms such as nitrogen, fluorine,hydrogen, or argon, or a combination thereof.

The graded germanium-containing layer 22 includes silicon, germanium,and oxygen. The atomic concentration of germanium decreases in thegraded germanium-containing layer 22 with the distance from thegermanium-containing layer 20. Thus, the atomic concentration ofgermanium in the graded germanium-containing layer 22 has variablevalues, which can be in a range from 0% and 99%. The atomicconcentration of germanium in the graded germanium-containing layer 22has a maximum value that is at least 50%, which occurs at or near theinterface with the germanium-containing layer 20. In one case, thegraded germanium-containing layer 22 can include germanium, silicon, andoxygen, and the sum of the atomic concentration of germanium, the atomicconcentration of silicon, and the atomic concentration of oxygen isgreater than 99% in each location within the graded germanium-containinglayer 22. The graded germanium-containing layer 22 may consistessentially of germanium, silicon, and oxygen, and the sum of the atomicconcentration of germanium, the atomic concentration of silicon, and theatomic concentration of oxygen is greater than 99% in each locationwithin the graded germanium-containing layer 22. In another case, thegraded germanium-containing layer 22 can include germanium, silicon, atleast another atom, and oxygen, and the sum of the atomic concentrationof germanium, the atomic concentration of silicon, the atomicconcentration of the at least another atom, and the atomic concentrationof oxygen is greater than 99% in each location within the gradedepitaxial germanium-containing layer 22. The graded germanium-containinglayer 22 may consist essentially of germanium, silicon, at least anotheratom, and oxygen, and the sum of the atomic concentration of germanium,the atomic concentration of silicon, the atomic concentration of the atleast another atom, and the atomic concentration of oxygen is greaterthan 99% in each location within the graded germanium-containing layer22. The at least another atom can be carbon, a p-type dopant such asboron, gallium, or indium, an n-type dopant such as phosphorus, arsenic,or antimony, any other impurity atoms such as nitrogen, fluorine,hydrogen, or argon, or a combination thereof.

In one embodiment, the germanium-containing layer 20 and the gradedgermanium-containing layer 22 are at least partially epitaxially alignedwith silicon substrate 10. The combined thickness of the stack of thegermanium-containing layer 20 and the graded germanium-containing layer22 is maintained not to exceed the critical thickness at which theepitaxial alignment between the single crystalline silicon substrate 10and the germanium-containing layer 20 is destroyed through stressrelaxation. In general, the thickness of the stack of thegermanium-containing layer 20 and the graded germanium-containing layer22 is between 5 nm and 100 nm, and preferably between 10 nm and 80 nm,although lesser and greater thicknesses can also be employed dependingon the concentration levels of germanium in the stack of thegermanium-containing layer 20 and the graded germanium-containing layer22, provided that the at least partial epitaxial alignment between thegermanium-containing layer 20, the graded germanium-containing layer 22,and the single crystalline silicon substrate 10 is maintained.

Optionally, the material stack including the single crystalline siliconsubstrate 10 and the stack of the germanium-containing layer 20 and thegraded germanium-containing layer 22 may be maintained at an elevatedtemperature for a period of time to enhance the degree of epitaxialalignment between the single crystalline silicon substrate 10 and thestack of the germanium-containing layer 20 and the gradedgermanium-containing layer 22 and/or to cure crystalline defects in thestack of the germanium-containing layer 20 and the gradedgermanium-containing layer 22.

Referring to FIGS. 2C, 2D, 2E, and 2F, the processing steps of FIGS. 1C,1D, 1E, and 1F are performed as in the first embodiment. At theprocessing step of FIG. 2C, the thickness of the at least partiallycrystalline silicon layer 30 is selected to apply sufficient stress tothe germanium-containing layer 20 to cause formation of a plurality ofcavities 27 within the germanium-containing layer 20 by the end ofdeposition of the at least partially crystalline silicon layer 30.Depending on the relative germanium concentrations in thegermanium-containing layer 20 and in the graded germanium-containinglayer 22 and the relative thicknesses of the germanium-containing layer20 and in the graded germanium-containing layer 22, the plurality ofcavities 27 may be formed solely within the germanium-containing layer20 or across the germanium-containing layer 20 and the gradedgermanium-containing layer 22.

The plurality of cavities 27 is formed during the growth of the at leastpartially crystalline silicon layer 30, i.e., before the completion ofdeposition of the silicon material of the at least partially crystallinesilicon layer 30. The lateral dimensions of the plurality of cavities 27is on the same order of magnitude as the combined thickness of thegermanium-containing layer 20 and the graded germanium-containing layer22. Typically, each cavity in the plurality of cavities has a maximumlateral dimension less than 200 nm. While the cleavage plane in FIG. 2Eis illustrated as passing only through the germanium-containing layer20, it is understood that the cleavage plane may pass through the gradedgermanium-containing layer 22 in some of the cases where the pluralityof cavities 27 is formed across the germanium-containing layer 20 andthe graded germanium-containing layer 22. Remnants of thegermanium-containing layer 20 and the graded germanium-containing layer22 are removed at the processing steps of FIG. 2F employing the samemethods as in the first embodiment.

Referring to FIGS. 3A, 3B, and 3C, a third exemplary semiconductorstructure according to a third embodiment of the present disclosure isthe same as the first exemplary semiconductor structure as shown inFIGS. 1A, 1B, and 1C, respectively, and can be formed by employing thesame processing steps.

Referring to FIG. 3D, a bonding material layer 42 may be employed tobond the at least partially crystalline silicon layer 30 to the handlesubstrate 40. The bonding material layer 42 can be a semiconductor oxidelayer form on the handle substrate 10 if the handle substrate includes asemiconductor material that can be converted into a semiconductor oxidesuch as silicon oxide or germanium oxide. Alternately, the bondingmaterial layer 42 can be an adhesive layer that includes resin, polymer,epoxy, or any other material that can be employed as an adhesive.

Referring to FIGS. 3E and 3F, the processing steps of FIGS. 1E and 1Fare performed as in the first embodiment.

Referring to FIGS. 4A, 4B, and 4C, a fourth exemplary semiconductorstructure according to a fourth embodiment of the present disclosure isthe same as the second exemplary semiconductor structure as shown inFIGS. 2A, 2B, and 2C, respectively, and can be formed by employing thesame processing steps.

Referring to FIGS. 4C, 4D, and 4F, the fourth exemplary semiconductorstructure according to the fourth embodiment of the present disclosurecan be formed employing the same processing steps as shown in FIGS. 3A,3B, and 3C, respectively, and can be formed by employing the sameprocessing steps.

Referring to FIG. 5, a graph of an X-ray diffraction data from a firstsample according to the first embodiment of the present disclosure isillustrated as a function of 2θ. Specifically, the first sample includesa stack of a handle substrate 10 and a at least partially crystallinesilicon layer 30 as illustrated in FIG. 1F. The handle substrate 10 hadan amorphous material (and thereby not contributing any sharp peak tothe X-ray diffraction data), and the at least partially crystallinesilicon layer 30 had a thickness of 300 nm. To manufacture the firstsample, a germanium-containing layer 20 (see FIGS. 1B-1D) consistingessentially of germanium and oxygen and having a thickness of 30 nm wasemployed. The single peak at 20 of approximately 69 degrees indicatesthat the at least partially crystalline silicon layer 30 within thefirst sample is a single crystalline silicon layer having a (100)surface orientation or a textured crystalline layer in which apredominant portion of grains is aligned along a (100) surfaceorientation and has a high quality of crystallinity.

Referring to FIG. 6, a graph of an X-ray diffraction data from a secondsample according to the second embodiment of the present disclosure isillustrated as a function of 2θ. Specifically, the second sampleincludes a stack of a handle substrate 10 and an at least partiallycrystalline silicon layer 30 as illustrated in FIG. 1F. The handlesubstrate 10 had an amorphous material (and thereby not contributing anysharp peak to the X-ray diffraction data), and the at least partiallycrystalline silicon layer 30 had a thickness of 120 nm. To manufacturethe second sample, a stack of an germanium-containing layer 20 and agraded germanium-containing layer 22 (See FIGS. 2B-2D) was employed. Thegermanium-containing layer 20 consisted essentially of germanium andoxygen and had a thickness of 30 nm. The graded germanium-containinglayer 22 consisted essentially of germanium, silicon, and oxygen, andhad a thickness of 50 nm. The single peak at 20 of approximately 69degrees suggests that the at least partially crystalline silicon layer30 within the second sample is a single crystalline silicon layer havinga (100) surface orientation or a textured crystalline layer in which apredominant portion of grains is aligned along a (100) surfaceorientation and has an even higher quality of crystallinity than thefirst sample of FIG. 5.

For illustrative purposes, an X-ray diffraction data from a third sampleincluding a polysilicon film as a function of 2θ is shown in FIG. 7. Thepolysilicon film of the third sample provided multiple peakscorresponding to various crystallographic orientations in the grains ofthe polysilicon film.

Referring to FIG. 8, a graph illustrates data from a secondary ion massspectroscopy (SIMS) run on the second sample of FIG. 6 prior tocleavage, i.e., the second sample according to the second embodiment ofthe present disclosure at the step of FIG. 2C. The atomic concentrationsof germanium, silicon, and oxygen are shown by three curves labeled“Ge,” “Si,” and “O,” respectively. The graph in FIG. 8 is divided intoportions corresponding to the various structural elements in the firstexemplary semiconductor structure of FIG. 2C, and each portion islabeled with the corresponding reference numeral in the first exemplarysemiconductor structure of FIG. 2C.

Referring to FIG. 9, a scanning electron micrograph (SEM) is shown of abroken portion of the first sample along a vertical cleavage plane at astep corresponding to FIG. 1C, i.e., prior to attaching a handlesubstrate 10 or cleaving along the oxygen-containing germanium layer 20.This SEM shows, from bottom to top, a vertical surface of a singlecrystalline silicon substrate 10 as cleaved for SEM preparation, avertical surface of an oxygen-containing germanium layer 20 as cleavedfor SEM preparation, and a vertical surface of an at least partiallycrystalline silicon layer 30 as cleaved for SEM preparation, and a topsurface of the at least partially crystalline silicon layer 30. Aplurality of cavities is shown in the oxygen-containing germanium layer20 in dark color.

Referring to FIG. 10, a scanning electron micrograph (SEM) is shown of aportion of the first sample, which was cleaved along a plane in theoxygen-containing germanium layer 20 at a step corresponding to FIG. 1E.This portion of the first sample includes a bulk silicon substrate 10and a portion of the oxygen-containing germanium layer 22, i.e., a lowergermanium-containing portion 27A. This SEM shows, from bottom to top, avertical surface of the single crystalline silicon substrate 10 ascleaved for SEM preparation, a vertical surface of the lowergermanium-containing portion 27A as cleaved for SEM preparation, and atop surface of the lower germanium-containing portion 27A. A pluralityof cavities is shown on the top surface of the lowergermanium-containing portion 27A in dark color.

While the present disclosure has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details can be made without departing from the spirit and scope ofthe present disclosure. It is therefore intended that the presentdisclosure not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of forming a semiconductor structure comprising: growing a germanium-containing layer on a single crystalline silicon substrate; growing an at least partially crystalline silicon layer on said germanium-containing layer; bonding a handle substrate to said at least partially crystalline silicon layer; and cleaving an assembly of said handle substrate and said at least partially crystalline silicon layer off said single crystalline silicon substrate along a plane in said germanium-containing layer.
 2. The method of claim 1, wherein said germanium-containing layer is grown in an ambient having an oxygen partial pressure at a level that incorporates oxygen into said germanium-containing layer at an atomic concentration between 1% and 50%.
 3. The method of claim 2, wherein said oxygen partial pressure is at a level that incorporates oxygen into said germanium-containing layer at an atomic concentration between 2% and 20%.
 4. The method of claim 1, wherein said germanium-containing layer has a thickness that is between 5 nm and 60 nm.
 5. The method of claim 1, wherein said germanium-containing layer consists essentially of germanium and oxygen, wherein a sum of an atomic concentration of germanium and an atomic concentration of oxygen is greater than 99%.
 6. The method of claim 1, wherein said germanium-containing layer includes germanium, silicon, and oxygen, wherein a sum of an atomic concentration of germanium, an atomic concentration of silicon, and an atomic concentration of oxygen is greater than 99%.
 7. The method of claim 1, wherein a plurality of cavities is formed within said germanium-containing layer before said cleaving of said assembly of said handle substrate and said at least partially crystalline silicon layer.
 8. The method of claim 7, wherein said plurality of cavities is formed during said growing of said at least partially crystalline silicon layer.
 9. The method of claim 7, wherein said plurality of cavities has a maximum lateral dimension less than 200 nm.
 10. The method of claim 1, wherein said at least partially crystalline silicon layer has a thickness that is greater than 100 nm before said bonding of said handle substrate to said at least partially crystalline silicon layer.
 11. The method of claim 1, wherein said handle substrate includes a dielectric material layer, a conductive material layer, a polycrystalline semiconductor material layer, a single crystalline semiconductor material layer, or a combination thereof.
 12. The method of claim 1, wherein said at least partially crystalline silicon layer is epitaxially grown directly on said germanium-containing layer, said germanium-containing layer being epitaxially aligned with said single crystal silicon substrate.
 13. The method of claim 12, wherein said germanium-containing layer has a substantially constant germanium concentration at an atomic concentration from 30% to 99%.
 14. The method of claim 12, further comprising epitaxially growing a graded germanium-containing layer directly on said germanium-containing layer, wherein said at least partially crystalline silicon layer is epitaxially grown directly on said graded germanium-containing layer, said graded germanium-containing layer includes silicon, germanium, and oxygen, and an atomic concentration of germanium decreases in said graded germanium-containing layer with a distance from said germanium-containing layer.
 15. The method of claim 14, wherein said germanium-containing layer has a substantially constant germanium concentration at an atomic concentration from 30% to 99%, and said graded germanium-containing layer has a germanium concentration that varies with said distance from said germanium-containing layer and has variable values in a range from 0% and 99%.
 16. The method of claim 14, wherein said germanium-containing layer includes silicon, germanium, and oxygen, and an atomic concentration of germanium decreases in said graded germanium-containing layer with a distance from said single crystalline silicon substrate and has variable values in a range from 0% and 99%.
 17. The method of claim 16, wherein said atomic concentration of germanium in said graded germanium-containing layer has a maximum value that is at least 50%.
 18. The method of claim 1, wherein a surface normal of a planar top surface of said silicon substrate has a set of Miller indices, wherein at least one Miller index in said set of Miller indices has an absolute value that exceeds
 6. 19. The method of claim 1, wherein said growing of said at least partially crystalline silicon layer on said germanium-containing layer is performed after said growing of said germanium-containing layer on said single crystalline silicon substrate.
 20. The method of claim 1, wherein said growing of said at least partially crystalline silicon layer on said surface of said germanium-containing layer comprises depositing said at least one partially crystalline semiconductor layer over said germanium-containing layer.
 21. The method of claim 1, wherein said growing of said germanium-containing layer on said single crystalline silicon substrate comprises depositing said germanium-containing layer directly on a surface of said single crystalline silicon substrate.
 22. The method of claim 1, wherein said at least partially crystalline silicon layer physically contacts said germanium-containing layer upon formation. 